Stabilized magnetic nozzle for plasma jets



July 12, 1960 v. H, BLACKMAN 2,945,119

STABILIZED MAGNETIC NozzLE FOR PLASMA JETS Filed Sept. 8, 1959 2Sheets-Sheet l Fb/ics. j.

sen/0N Af. 5f. 4m/M4N INVENTOR.

July 12, 1960 v. H. BLACKMAN STABILIZED MAGNETIC NOZZLE FOR PLASMA JETSFiled sept. e, 1959 2 Sheets-Sheet 2 SOl/@CE caPefA/r soa/Pcf a6 nitedStates Patent O Plasmadyne Corporation, Santa'Ana, Calif., a corporationof California Filed sept. s, 1959, ser. No. 838,692

1o claims. (c1. :19.-12er This invention relates to stabilized magneticnozzle means for an ionized gas ow, and also relates to an electricalplasma-jet torch incorporating auxiliary arcing means for purposes ofstabilizing the jet and increasing the energy thereof.

An object of the present invention is to provide an electricalplasma-jet torch incorporating a magnetic nozzle means which isstabilized through use of an auxiliary electric arc.

Another object is to provide stabilizing means for ionized gas flows,and employing combination magnetic and electric-arc elfects forstabilizing the flow, increasing the stagnation enthalpy thereof, andincreasing the life of the electrodes.

A further object of the invention is to provide magnetic nozzle meansstabilized by a longitudinally-directed electric arc, in combinationwith means for effecting rotation of the terminals of the arc in orderto augment the stabilization effect and increase electrode life.

These and other objects and advantages of the invention will be setforth more fully in the following specitication and claims, consideredin connection with the attached drawings to which they relate.

In the drawings:

Figure 1 isi a longitudinal sectional view illustrating schematically afirst form of apparatus for stabilizing and adding energy to the ionizedgas emanating from a plasma-jet torch;

Figure 2 is a transverse section taken on line 2--2 of Figure 1;

Figure 3 is a view, partially in longitudinal central section andparti-ally in side elevation, illustrating a second embodiment of theinvention in which magnetic means are provided to insu're rotation ofthe terminal portions of the stabilizing arc and thereby providedesirable results including increased electrode life; and

Figure 4 is an enlarged view of the right portion of the showing ofFigure 3, illustrating representative lines of magnetic force and alsoillustrating the stabilizing arc and the rotation thereof.

Referring first to the embodiment of Figures 1 and 2, a stabilizedmagnetic nozzle means is illustrated as employed in stabilizing andadding energy to the plasma jet 11 (composed of neutral gas, ions andelectrodes, at high temperatures) emanating from an electricalplasma-jet torch 12. The illustrated torch 12 comprises a generallycup-shaped metal nozzle electrode 13 having a generally disc-shapedmetal back electrode 14 mounted therein in insulated relationship.Nozzle electrode 13 and back electrode 14 cooperate to define an annulargas-pressure chamber 16 which is coaxial with the nozzle opening 17 inthe nozzle electrode. The wall of nozzle opening 17 is protected by agenerally tubular refractory metal insert 18, formed of tungsten orthelike, and the adjacent arcing portion of the back electrode issimilarly provided with a disc-shapedtungsten insert 19.

A anged metal base member 21 is disposed in surface engagement with theperipheral portion of back electrode atente July 12, 1960 r* ICC 14,such elements being maintained in surface engagement by means of aretaining ring 22 which is threaded into the nozzle electrode. Suitableinsulation means 23 are provided to maintain the base member 21 and backelectrode v14 electrically insulated from nozzle electrode 13. Coolingchambers 24 and 25 are formed, respectively, adjacent the arcing inserts18 -and 19 in the electrodes in order to effect cooling thereof. Watermay be passed continuously through chambers 24 and 25 by means of theindicated passages and hoses.

A suitable current source 26 is electrically connected between basemember 21 and nozzle electrode 13 in order to conduct current to thearcng inserts 18 and 19 of the nozzle and back electrodes. An arc may beinitiated between such inserts in any suitable manner, as by momentarilyimpressing a high voltage therebetween. The arc effects heating of gaswhich is introduced into the gas-pressure chamber 16 from a suitablesource 27 through a passage 28 which is tangential to the chamber 16.Gas enters chamber 16 at suificient velocity and pressure to owvortically therein and effect stabilization of the-arc in the axialcanal through the vortex. The gas is ionized and greatly heated by thearc, and discharges axially out nozzle opening 17 (in the form of jet11) into the magnetic nozzle means 10 next to be described. Y

The magnetic nozzle means 10 comprises a relatively short helicalcurrent-conducting coil 31 mounted co- Aaxially around the plasma jet 11emanating from torch 12 and adapted, when supplied with a large currentfrom a suitable direct current sourcey 32, to generate a magnetic iieldhaving strong axial and radial components. Stated otherwise, thegenerated magnetic field is generally nozzle-shaped and provides anozzle action with relation to the ionized plasma jet 11 passingcoaxially therethrough. Wall means 33 are shown provided around the coil31 in order to define a cooling chamber through which water may bepassed by means of conduits 34. The magnetic nozzle having strong axialand radial components is described in co-pending patent applicationSerial No. 775,973, filed November 24, 1958, for High- IntensityElectrical Plasma-I et Torch Incorporating Magnetic Nozzle Means,inventors Gabriel M. Giannini and Vernon H. Blackman, and assigned tothe assignee of the present invention.

Electrode elements 36 and 37 are mounted in mutuallyinsulatedrelationship around the plasma jet 11 at opposite ends of coil 31 inorder to form an electric arc 38 passing through the jet. In theillustrated apparatus, each electrode 36 and 37 comprises a short metaltube which is mounted in flush relationship in an elong-ated insulatingtube 39 which may be formed of quartz or the like. The inner end of tube39 is ush with the outer end of insert 18, so that the plasma jet 11 isunimpeded as it leaves the torch 12 and passes through the tube 39 aswell as the electrodes 36 and 37 interposed therein.

A direct current source 41 is connected to the electrodes 36 and 37 inorder to supply current thereto so that the current may pass, in theform of an arc, between the electrodes 36 and 37 and longitudinally ofthe central portion of insulating tube 39. Arcing is enhanced because ofthe ionized condition of the plasma jet 11. In order to increase thearcing action, small metal protrusions may be provided on the internalsurfaces of electrodes 36 and 37 at circumferentially spaced points.

In the operation of the embodiment of Figures 1 and 2, a strong directcurrent is fed from source 32 to winding 31 in order to generate thedescribed magnetic tield having strong axial and radial components.Direct current is also fed from source 41 to electrodes 36 and 37, and

the arc v38 is initiated therebetween longitudinally through the plasmajet and through the central portion of insulating tube 39.

The presence of the electric arc 38 within the magnetic nozzle formed bywinding 31 eliminates or minimizes any tendencyof the plasma v111 tobecome unstable be cause of the presence -of disturbances along thesurface of the flow, or other factors. The arc 38 also greatly increasesthe energy (stagnation enthalpy) of the plasma.

The stabilization indicated'above is believed to result from acombination of the generally longitudinal magnetic field generated bywinding 31 and the circumferen- -tial magnetic field generated by arc38. These combine to produce a rotating magnetic field having thedesired stabilizing characteristics. Such rotating magnetic field notonly effects plasma stabilization, but also tends to rotate the terminalportions of the arc 38, at electrodes 36 and 37, thereby preventing theare from burning into the electrodes and reducing the life thereof.

Embadment of Figures 3 and 4 Referring next to the second embodiment ofthe invention, illustrated in Figures 3 and 4, the plasma torch 12 maybe the same as in the previous embodiment and has been given the samereference numerals. The quartz tube 39, electrodes 36 and 37, currentsources 26 and 41, and winding 31 are also employed in the embodiment ofFigures 3 and 4.

In the present embodiment, two additional helical coils or windings 43and 44 are mounted coaxially around the inner and outer sections ofinsulating tube 39 and on opposite sides of electrodes 36 and 37 fromwinding 31. A shield 46, formed of soft iron or other magnetizablematerial, is mounted adjacent the forward wall of torch 12 in order toprevent entrance of lines of magnetic force `into the body of the torch.Suitable wall means 47 and 48 are provided around windings 43 and 44 toform water chambers through which water may be passed by means ofpassages, not shown. A direct current source 49 is employed to passcurrent through the windings 31, 43 and 44.

In the operation of the embodiment of Figures 3 and 4, current is fedfrom source 49 to the three magnetizing coils 31, 43 and 44 in order togenerate the previouslydescribed magnetic fields having portionsdisposed in the tube 39 and in electrodes 36 and 37. Representativelines of force in the magnetic fields generated by coils 43 and 44areindicated at 51 and 52 in Figure 4. The lines of force generated bythe winding 31 are not illustrated, in order to prevent confusion withthe representation 38 of the electric arc -between electrodes 36 and 37.

In normal operation, a relatively high current is fed to the centralwinding 31 in order to provide a strong magnetic nozzle effect. Theplasma passing through such magnetic nozzle is stabilized, as describedabove, by means of the electric arc 3S extending longitudinally of tube39 `between electrodes 36 and 37.

The windings 43 and 44 are normally supplied with smaller currents thanwinding 31, but such smaller currents are adequate to insure that theterminal portions of arc 38 will rotate around the common axis ofelectrodes 36 and 37 in order to provide a current-sheet effect or atleast prevent burning in of the terminal arc portions and consequentreduction in electrode life. The polarities of windings 43 and 44 arepreferably so selected that the terminal arc portions rotate in the samedirection, that is to say both clockwise or both counterclockwise asviewed from the right in Figure 4. The arrows 53 in Figure 4 indicate aclockwise rotation asA viewed from the right, such rotation resultingfrom the combination of the circumferential magnetic field generated byarc 38 and the generally longitudinal magnetic field generated by coil43.

If desired, the currents .fed through windings 43 and 44 may be asstrong or stronger than the current fed towinding 31, to provide threemagnetic nozzles in series relationship.A

-dition to what'has been illustratedv and described in'detail, may beemployed without departing from the scope of the accompanying claims.

I claim:

l. Stabilized magnetic nozzle means for a substantially arc-free streamof 'ionized gas, which comprises meansto create a'magnetic field throughwhich said stream passes, rand means to maintain an electric arc in saidstream adjacent said magnetic field.

2. Stabilized magnetic nozzle means for a jet of plasma, which comprisesmeans to create around saidjet a nozzleshaped magnetic field, and meansto maintain an electric arc lthrough said iet at said field,said-electric arc cooperating with said field to stabilize said jet.

3. Stabilizedmagnetic nozzle' means for an external jet of plasma from aplasma generator, which comprises a magnetizing winding mountedrelatively closely around said jet and adapted when supplied with directcurrent to form a magnetic field having strong components axially andradially of said jet, first and second electrodes provided in mutuallyinsulated relationship at longitudinal points along said jet andonopposite sides of said Winde ing, and means to maintain an electric arcbetween said electrodes and longitudinally through said jet.

4. Stabilizedmagnetic nozzle means lfor an external jet of plasma from aplasma generator, which comprises a magnetizing winding mountedrelatively closely around said jet and adapted when supplied with directcurrent to form a magnetic field having strong components axially andradially of said jet, first and second electrodes prol vided in mutuallyinsulated relationship at longitudinal points along said jet and' onopposite sides of said winding, means to maintain an electric arcbetween said electrodes and longitudinally through said jet, and meansto effect continuous movement of the terminal portions of said arcrelative to said electrodes to thereby prevent said terminal portionsfrom burning into said electrodes and reducing the life thereof. 'Y

5. An electrical plasma-jet torch apparatus, which comprises means togenerate a high-temperature jet of ionized gas, conduit means to confinesaid jet, firstand second generally 'annular electrodes provided atspaced points along said conduit means generally vcoaxially with saidjet, means to supply direct current to said electrodes to effect arcingtherebetween through said jet, and means to generate a magnetic eldadapted to effect rotation of the terminal portions of said arc aroundsaid electrodes.

6. An electrical plasma-jet torch apparatus, which comprises means togenerate a high-temperature jet of ionized gas, conduit means to confinesaid jet, first and second electrodes provided at spaced points yalongsaid conduit means, means to supply current to` said electrodes toeffect arcing therebetween through said jet, a mag- Vnetizing windingmounted around said conduit means generally coaxially of said jet andbetween said electrodes, and means to supply current to said winding tothereby generate a magnetic field through which said jet must pass.

7. An electrical apparatus, which comprises means-to generate ahigh-temperature jet or stream of ionized gas, first and secondgenerally annular electrodes provided at spaced points along said jetgenerally coaxially therewith, means to supply current to saidelectrodes to effect arcing therebetween through said jet, andmagnetizing means mounted around said jet adjacent said electrodes andadapted upon supply of current thereto to create magnetic nozzles forsaid jet and insure rotation of the terminal portions of the arc aroundsaid electrodes.

8. An electrical plasma-jet torch apparatus, comprising a nozzleelectrode having a nozzle opening therein, la back electrode spaced andinsulated from said nozzle electrede, meansto define an annulargas-pressure chamber between said electrodes and coaxial with saidopening,

means to introduce gas tangentiallgr into saidchamber for vortical owtherein and subsequent discharge through said opening, means to maintainan electric arc between said electrodes and inthe vicinity o'f saidopening in order to heat said gas and eect discharge of a jet of plasmaout said opening, rst and second electrodes mounted adjacent said jet inspaced and mutually insulated relationship, means to maintain anelectric arc through said jet between said electrodes, a relativelyshort helical magnetizing coil mounted coaxially around said jet betweensaid electrodes, and means to supply a strong direct current to saidcoil to elect generation in said jet of a magnetic eld having strongaxial and radial components.

9. An electrical plasma-jet torch apparatus, comprising a nozzleelectrode having a nozzle opening therein, a back electrode spaced andinsulated from said nozzle electrode, means to define a gas-pressurechamber between said electrodes and coaxial with said opening,

means to introduce gas into said chamber for discharge i through saidopening, means to maintain an electric arc between said electrodes andin the vicinity of said open ing in order to heat said gas and effectdischarge of a high-temperature jet of plasma out said opening, conduitmeans disposed on the side of said nozzle opening remote from said backelectrode to conne said jet of plasma, first and second annularelectrodes mounted in said conduit means coaxially thereof inlo'ngitudinally spaced and mutually insulated relationship, means tomaintain an electric arc between said annular electrodes andlongitudinally through said conduit means, a relatively short helicalmagnetizing coil mounted coaxially around said conduit means betweensaid annular electrodes, and means to supply a strong direct current to'said coil to effect generation in said conduit means of a magnetic eldhaving strong axial and radial components.

10. The invention as claimed in claim 9, in which second and third coilsare mounted coaxially around said conduit means respectively adjacentsaid annular electro'des, and means are provided to supply directcurrent to said second and third coils to effect generation of magneticelds in said conduit means and eect rotation of the terminal portions ofsaid arc around said annular electrodes.

References Cited in the file of this patent UNITED STATES PATENTS1,963,869 Sandelowsky et al June 19, 1954 2,768,279 Rava Oct. 23, 19562,806,124 Gage Sept. 10, 1957

